You also cannot directly compare a metro line to intercity rail. That line in Tokyo was like what, 20th they built all in the same terrain, they are really good at this by now. Meanwhile, rail tunnels are usually bespoke projects.
But there was a war, wasn't there? So why not admit that 8000-year-old myth can have got "the rocks went flying" part right.
Written accounts are still vastly superior to oral tradition of course, their accuracy is on another level. But that doesn't mean there is absolutely nothing to glimpse from old myths.